There are a couple of ways for me to suggest what to do...one would be for you to pencil out a plan of boxes(squares), if that is what you want and size to get an idea for the fish:)Then I'd go fishing for fishes...online, coloring books..conservation sites, etc. And make the fish you want w/different fabrics and wonder under w/a straight stich(or satin stitch, etc) on each fish. Then put then in the designated squares. You would make the fish to fit whatever size you came up with. I'm sure there are favorite fish of his:)Or you can put a fish in the center...whatever size you decide w/colors of the fish all the way around him in quilt blocks. Just some thought on this:)Skeat (or use actual fishing pictures of caught fish from him for your blocks:)

Are your blocks all different sizes? Well it would work the same if they are all the same size to. Just put various sized sashing ,or coping strips, around your blocks. I think it is easiest to break it down into sections.
Say 5 or 6 blocks, arrange them the way you want with different size sashings. then on the next section you want to make it about the same size and just keep fitting the sections together. I know I am not explaining this very well. Here is the link to my chicken quilt maybe you can see how I did it. but I think you would want all the same color sahsings on yours.http://www.quiltingboard.com/posts/list/17004.page

Sewnsewer, that quilt was a t-shirt quilt and probably done with fusible web. The t-shirt fabric was backed with a fusible web of somekind, the square cut out (or vice-versa) and then ironed onto the fabric. It looks like the background fabric is all one piece, not pieced (?huh?). You could do your fish like that, or piece borders around them.

If you have the size of the blocks and you know the size of the finished quilt. I would mark the outline of the quilt on a piece of grid paper. I would lay out the individual squares within the outline until I was happy with the look and then I would measure the size of the sashing to match. Grid paper gives you the finished size so I would need to add 1/2' for seam allowance.